Combined refrigeration and power plant

ABSTRACT

A combined refrigeration and power plant. The power plant comprises an internal combustion engine an air cycle machine refrigerator driven by the internal combustion engine and configured to refrigerate atmospheric air to provide working fluid to combined refrigeration and power generation cycle, a refrigerated air storage unit configured to store working fluid produced by the air cycle machine refrigerator; and first and second heat exchangers. The first heat exchanger arrangement is configured to exchange heat between a device to be cooled and the working fluid, and the second heat exchanger arrangement is configured to exchange heat between the working fluid downstream of the first heat exchanger in the combined refrigeration and power generation cycle and waste heat from the internal combustion engine; and a generator turbine configured to receive heated working fluid from the second heat exchanger arrangement, and configured to power an electrical generator.

The present disclosure concerns a combined heating and refrigeration power plant.

Large industrial equipment such as large computing facilities frequently requires both electrical power and refrigeration or cryogenic cooling. In a known prior system, both electrical power and cooling are provided by a combined refrigeration and power plant. Typically, such plants comprise mechanical power plant such as a reciprocating internal combustion engine which drives an alternator to provide electrical power. The engine also provides input power to a closed cycle mechanical refrigerator, which provides coolant. Alternatively or in addition, waste heat from the engine exhaust may be used to lower the temperature of the coolant using an absorption chiller. In some cases, the above equipment is operated only in the event of main electrical grid failure, with normal operation being provided using electrical power from the main electrical grid.

However, such a system is inefficient, leading to high fuel costs and high emissions. Furthermore, the internal combustion engine must run continually in the event of a main electrical grid failure, leading to increased engine wear and maintenance costs.

Accordingly, the present invention seeks to provide a combined refrigeration and power plant that overcomes some or all of the above problems.

According to a first aspect there is provided a combined refrigeration and power plant comprising:

-   -   an internal combustion engine;     -   a refrigerator driven by the internal combustion engine and         configured to refrigerate a working fluid of a combined         refrigeration and power generation cycle;     -   a refrigerated working fluid storage unit configured to store         working fluid produced by the refrigerator;     -   a first heat exchanger arrangement configured to exchange heat         between a device to be cooled and the working fluid;     -   a second heat exchanger arrangement configured to exchange heat         between the working fluid downstream of the first heat exchanger         in the combined refrigeration and power generation cycle and         waste heat from the internal combustion engine;         an electrical generator; and         a generator turbine configured to receive heated working fluid         from the second heat exchanger arrangement, and configured to         power the electrical generator.

Advantageously, in the event that the combined refrigeration and power plant is required, both cooling and electrical power can be provided using the generator turbine using the heat difference between the device to be cooled and the working fluid. Once the working fluid store is depleted, the internal combustion engine can be used to top up the working fluid store. Consequently, waste heat from the device to be cooled is utilised in the thermodynamic cycle, thereby increasing efficiency, while power and cooling can be provided without requiring continuous operation of the internal combustion engine.

The refrigerator may be configured to liquefy the working fluid prior to delivery to the refrigerated working fluid storage unit. Advantageously, the working fluid storage unit can be relatively compact in view of the large exergy of liquid working fluids compared to gaseous working fluids.

The internal combustion engine may comprise one or more of a gas turbine engine and a reciprocating engine. Alternatively, the internal combustion engine may comprise a rotary engine such as a Wankel engine.

The second heat exchanger arrangement may comprise a plurality of heat exchanger matrices, each being configured to exchange heat between the working fluid and a separate heat source of the internal combustion engine. The second heat exchanger arrangement may comprise a first matrix configured to exchange heat between engine cooling water and the working fluid and may comprise a second matrix configured to exchange heat between engine cooling oil and the working fluid.

The reciprocating engine may comprise a turbocharger and may comprise an aftercooler. The second heat exchanger arrangement may comprise a third exchanger matrix configured to exchange heat between the turbocharger aftercooler and the working fluid, and may comprise a fourth heat exchanger matrix configured to exchange heat between the turbocharger compressor outlet and the working fluid, and may comprise a fifth heat exchanger matrix configured to exchange heat between the turbocharger turbine inlet and the working fluid. The working fluid may be arranged to exchange heat between the first, second, and, where present, third, fourth and fifth heat exchangers in series. Advantageously, maximum heat is absorbed from the reciprocating engine for delivery to the generator turbine, thereby maximising thermal efficiency.

The power plant may comprise a third heat exchanger arrangement configured to exchange heat between working fluid downstream of the working fluid storage unit and upstream of the first heat exchanger, and working fluid downstream of the generator turbine and upstream of the liquid air storage unit. Consequently, heated working fluid from the generator turbine exhaust is cooled before being returned to the working fluid storage unit, thereby reducing working fluid losses, while increasing the temperature of the working fluid prior to exchanging heat between the first and second heat exchanger, thereby increasing electrical power generation capacity. Alternatively, the third heat exchanger may be configured to exchange heat between working fluid downstream of the first heat exchanger and upstream of the second heat exchanger, and working fluid downstream of the generator turbine and upstream of the working fluid storage unit.

The internal combustion engine may comprise an internal combustion engine drive shaft mechanically coupled to the generator turbine. Advantageously, the generator turbine output power can be increased using mechanical power from the internal combustion engine.

The refrigerator may comprise an air cycle machine refrigerator comprising a Brayton cycle machine comprising a compressor configured to compress air, and a turbine configured to expand compressed air, the compressor and turbine being coupled by an air cycle machine shaft. The air cycle machine refrigerator may further comprise a fourth heat exchanger configured to exchange heat between air downstream of the compressor and upstream of the turbine, and a cold sink.

The cold sink may comprise a heat storage unit, or may comprise the working fluid downstream of the device to be cooled and upstream of the internal combustion engine.

The air cycle machine shaft may be coupled to the internal combustion engine drive shaft. The air cycle machine shaft may be coupled to an electrical motor, which may be electrically couple to a main electrical grid. Advantageously, the air cycle machine can be driven by one or both of the internal combustion engine and electrical power from the main electrical grid. The power plant may comprise a clutch such as a freewheel clutch configured to selectively disengage the air cycle machine shaft from the electrical generator.

The working fluid storage unit may comprise a pressure vessel configured to accept working fluid downstream of the refrigerator, and deliver working fluid to one of the first and the third heat exchanger.

The working fluid storage unit may comprise a separator configured to separate liquid and gaseous working fluid phases. The separator may be configured to deliver gaseous phase working fluid to one or more of an outlet valve and a refrigerator inlet.

The working fluid may comprise one of atmospheric air and supercritical carbon dioxide.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Embodiments will now be described by way of example only, with reference to the Figures, in which:

FIG. 1 is a schematic illustration of a combined refrigeration and power plant in accordance with the present disclosure;

FIGS. 2a-c are schematic illustrations of the combined refrigeration and power plant of FIG. 1 operated in accordance with first, second and third operating modes respectively.

With reference to FIG. 1, a combined refrigeration and power plant 10 is provided. The power plant 10 is configured to provide electrical power from a first electrical power output connection 12, which is electrically coupled to a main electrical power grid. The power plant is further configured to provide electrical power to onsite equipment 14 via a second electrical connector 13. The power plant 10 is further configured to also provide low temperature coolant to onsite equipment 14, such as air conditioning equipment, or computer server equipment via a first heat exchanger arrangement 15. It will be understood that the figures are not to scale, and do not necessarily represent the physical layout of the disclosed system, but rather the interrelations of the various components.

The power plant 10 comprises an internal combustion engine in the form of a turbocharged, after-cooled reciprocating engine 16 such as a Diesel or Otto cycle engine, and could be configured to operate on any suitable fuel, such as petrol, diesel or natural gas. The engine 16 is of conventional construction, comprising moveable pistons within a cylinder (not shown), which are arranged to drive an output shaft 18. It will be understood that the engine could alternatively comprise a rotary engine such as a Wankel engine. The engine 16 is provided with inlet air 20 from a turbocharger compressor 22. The turbocharger compressor 22 is driven by a turbocharger turbine 24 via a shaft 25, the turbine 24 being driven by exhaust gasses 26 from the internal combustion engine 16. Between the turbocharger compressor 22 and the engine intake is an after-cooler 24, which cools the intake charge prior to delivery to the cylinder, to increase charge density and so power. Where the internal combustion engine 16 is spark ignition engine, the after-cooler may also help prevent knock.

The internal combustion engine is provided with cooling systems to manage heat. A liquid cooling system (such as a water/glycol system) is provided, comprising a water jacket (not shown) surrounding the cylinders. The liquid cooling system comprises an engine main cooling radiator 28, which is configured to reject waste heat from the engine cylinders. Similarly, the engine comprises an oil cooling system comprising an oil radiator 30 configured to reject waste heat from engine lubricating oil. An after-cooler cooling system is also provided, which again comprises an after-cooler radiator 32 configured to reject heat from the intake charge prior to delivery to the engine inlet. A turbocharger outlet heat exchanger 34 is also provided, which absorbs heat downstream of the turbocharger 24 outlet. Finally, a turbocharger turbine inlet heat exchanger 36 is provided, which absorbs heat upstream of the turbocharger 24 turbine inlet.

The power plant 10 further comprises an electrical generator 38. The generator 38 is of any suitable type, and is configured to provide electrical power to the electrical power output connection 12. The electrical generator 38 is driven by a generator input shaft 40, which is in turn coupled to a generator turbine 42. The input shaft 40 is also coupled to the combustion engine drive shaft 18 by a gear arrangement 44, which may provide reduction or step-up gearing, and may be in the form of a bevel gear arrangement, a belt drive, or a hydrostatic arrangement. A clutch 19 is provided to selectively couple the shafts 18, 40. It will be understood however that the shafts 18, 40 may be directly coupled, and may comprise the same shaft. In the described embodiment, a hydrostatic fluid coupling 74 is provided, so that the output speed of the internal combustion engine does not have to be matched to the electrical frequency of the grid power.

The shaft 40 is further coupled to a shaft 46 of a refrigerator in the form of an air cycle machine 45 via clutch 48. The clutch may be actively engaged and disengaged, or may comprise an overrunning clutch such as a sprag clutch. The air cycle machine comprises an air cycle machine compressor 50 and an air cycle machine turbine 52 interconnected by the air cycle machine shaft 46. The air cycle machine further comprises an air cycle machine heat exchanger 54 having a hot side provided in working fluid flow between the air cycle machine compressor 50 and turbine 52, and configured to exchange heat from compressed working fluid with a cooling medium 56. The cooling medium 56 is cycled through a fifth heat exchanger 84, which exchanges heat between the cooling medium 56 and the working fluid between the first and second heat exchanger arrangements 15, 27.

The air cycle machine shaft 46 is also coupled to an electrical motor 58, which is configured to drive the shaft 46. The electric motor is supplied with electrical power from the main electrical grid via a grid input connection 60, and from the generator 38 via an electrical connection 17.

The power plant further comprises a working fluid storage unit in the form of a separator pressure vessel 62 configured to store a working fluid in the form of air in either or both of a liquid and a gaseous phase. The pressure vessel 62 is configured to separate liquid and gaseous phases of the working fluid. A liquid phase pump 76 is provided downstream of the pressure vessel 62, and is configured to receive liquid phase working fluid from the pressure vessel 62.

The power plant also includes a third heat exchanger 66 comprising a cold side provided downstream of the pressure vessel 62 and upstream of the first heat exchanger 15 in working fluid flow 64.

In operation, working fluid flows throughout the working fluid line 64 as follows. Starting from an ambient air inlet 68, air is ingested into an inlet of the air cycle machine compressor 50 and is thereby compressed and heated in a gaseous phase. Compressed air from the compressor 50 is directed to the hot side of the air cycle machine heat exchanger 54, and is thereby cooled by lower temperature coolant medium 56. The working fluid is then directed to an inlet of the air cycle machine turbine 52, which expands and thereby further cools the working fluid in the line 64. In view of the energy extracted by the turbine 52, and the shaft 46 interconnecting the turbine 52 to the compressor 50, fluid flow through the air cycle machine drives the compressor 50.

From the turbine 52 outlet, working fluid is directed to the separator pressure vessel 62, where it can be stored for further use. The output of the turbine 52 may be of varying pressures and temperatures in view of varying ambient temperatures and working fluid temperatures at the turbine inlet, and consequently the working fluid may comprise a gaseous phase, a liquid phase, or a combination of the two. Consequently, liquid phases are allowed to settle within the pressure vessel. The vessel 62 is provided with a first gaseous outlet line 68, which communicates with the inlet of the air cycle machine turbine 50. Consequently, higher temperature gaseous phase air can be recycled, and the temperature lowered further. A second gaseous outlet line 70 is provided, which can be used to exhaust gaseous air to the atmosphere in the event that the pressure within the system exceeds a safe limit.

The vessel 62 further comprises a liquid phase outlet line 72, through which liquid air is passed further downstream to a cold side of the third heat exchanger 66, whereupon the working fluid in line 72 is heated to a temperature that may be above the boiling point of the working fluid at the temperatures within line 72.

The working fluid then continues to the first heat exchanger arrangement 15, where the working fluid is used to cool electrical equipment 14, thereby providing refrigeration.

Downstream in working fluid flow of the first heat exchanger arrangement 15 is a second heat exchanger arrangement 27 comprising the internal combustion engine heat exchangers 28, 30, 32, 34, 36. A cold side of each heat exchanger 28, 30, 32, 34, 36 is provided in working fluid flow series, such that the working fluid is gradually heated as it progresses through the heat exchangers 28, 30, 32, 34, 36. Since the heat exchangers are arranged in order of the temperatures of the fluids of the hot side of the respective heat exchangers 28, 30, 32, 34, 36, the temperature of the working fluid is increased at each stage, while the cooling fluid of the hot side of each respective heat exchanger is cooled.

After the final heat exchanger stage 36 of the second heat exchanger arrangement 27, the now hot, gaseous working fluid is passed to an inlet of the generator turbine 42, whereupon the working fluid is expanded, to thereby drive the turbine 42. Working fluid is then passed from outlet of the turbine 42 to a hot side of the third heat exchanger 66, where heat is transferred to the cold side, as described above. The working fluid is then passed to the air cycle compressor 50 inlet, where the cycle is repeated. Typical temperatures of the various fluids and working fluid at each stage in the cycle are shown in the drawing. In some modes of operation, the working fluid between the third heat exchanger 66 and the air cycle machine compressor 50 may still be relatively cool, and so a return line 78 is provided, which allows working fluid to bypass the air cycle machine 45, and return directly to the pressure vessel 62. The line 78 comprises a throttle 80 to expand the working fluid in the line 78, to thereby liquefy a portion fo the working fluid prior to return to the pressure vessel 62. Suitable valves (not shown) are provided to control flow to either the air cycle machine compressor 50 or the pressure vessel 62 via the return line 78. First and second dump valves 82, 84 is also provided upstream and downstream of the compressor 50 respectively, to control pressure within the system.

Motive power for the above cycle can be provided for in various ways in accordance with one of a first, second or third operating mode, as described hereinbelow with reference to FIGS. 2a to 2c respectively. In FIGS. 2a-c , the working cycle is simplified, though it will be understood that each of the components shown in FIG. 1 are still present.

As shown in FIG. 2a , in the first operating mode, grid input 60 and output connections 12 are connected to the grid network. Consequently, electric motor 58 is operated to drive shaft 46, and so drive the air cycle machine compressor 52 (not shown in FIG. 2a ). Consequently, heat is expelled from the working fluid by the air cycle machine, and so cooled to cryogenic temperatures being delivered to the pressure vessel 62 for use in cooling the equipment 14, as described above.

Meanwhile, the clutch 19 is disengaged, and the internal combustion engine 16 is inoperative. The clutch 48 is also disengaged. However, in view of the heated working fluid flowing through the generator turbine 42, the generator 38 is driven to provide electrical power to the grid through connection 12. In particle, the expansion of the working fluid from the liquid to the gaseous phase increases the pressure within line 64 to around 2×10⁷ Pascals, thereby providing sufficient pressure to power the generator turbine 42, at relatively low temperatures.

As shown in FIG. 2b , in the second operating mode, both grid connections 12, 60 are not available. Working fluid from the pressure vessel 62 continues to be provided to the first heat exchanger, and thus the equipment is still cooled. Meanwhile, power is produced by the generator turbine 42 in view of expansion within the turbine 42, which is then provided to the equipment 14 to thereby electrically power the equipment. Since the turbomachinery 42, 52, 68 and generator 38 are already in operation when switched from the first mode to the second mode, no interruption in either refrigeration or electrical power generation is experienced by the equipment 14.

As heat is rejected to the working fluid by the equipment, the proportion of gaseous working fluid to liquid working fluid increases, as does the pressure. Consequently, spent working fluid may be vented through line 70.

Eventually, the liquid working fluid will be spent, and the power output to the generator 38 will decrease. At this point, the system is operated in the third mode, as shown in FIG. 2c . In the third mode, the internal combustion engine 16 is started, and the clutch 19 is closed. Consequently, the generator turbine 42 is directly driven to provide electrical power to the equipment. The clutch 48 is also closed, to drive the air cycle machine shaft 46, to thereby provide cooled working fluid to the equipment 14, and thereby provide refrigeration. Consequently, both cooling and electrical power continues to be provided, again, without any interruption. Excess electrical power from the generator 38 may be transferred to the electrical motor 58 to provide additional cooling where required, to “top up” the working fluid. Consequently, the system is relatively robust in the event that the internal combustion engine 16 also fails.

Consequently, a combined refrigeration and power plant is disclosed, which is highly efficient, whilst also providing robustness in the event of failure. The system can cope with short term loss of grid connection without requiring operation of the internal combustion engine, and can provide uninterrupted cooling and electrical supply without a requirement for electrical storage.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

For example, the system could comprise an absorption chiller configured to absorb waste heat from the internal combustion engine, and cool the working fluid at an appropriate point in the cycle. One of the generator and the motor could be omitted, since the remaining electrical machine could be operated as either a motor or a generator as required. The third heat exchanger could be provided in a different location within the working fluid flow, such as between the first and second heat exchanger arrangements.

The power plant could comprise a further waste heat recovery engine, such as a power turbine, steam turbine or Stirling engine driven by heat from internal combustion engine exhaust gasses. The system could comprise a combustor configured to combust fuel with air within the working fluid line upstream of the generator turbine.

The working fluid line may comprise one or bypass lines configured to bypass working fluid around one or more heat exchangers. The power plant may comprise a plurality of internal combustion engines, and may comprise a mixture of piston, rotary and gas turbine engines. The air cycle machine may comprise a vapour-compression cycle comprising an expansion valve in place of the air cycle turbine, a vapour absorption cycle, or any other suitable refrigeration cycle employing air as the working fluid.

The power plant may comprise electrical storage electrically coupled to at least the electrical generator and to the device to be cooled. The electrical storage may be electrically coupled to the electrical motor (where present), and to the working fluid pump (where present). The electrical storage could comprise a chemical battery, or a fuel cell.

The internal combustion engine could comprise a gas turbine engine, which could be recuperated and/or intercooled. The second heat exchanger arrangement could comprise the intercooler and recuperator heat exchangers.

The working fluid could comprise any suitable working fluid that, such as carbon dioxide.

The device to be cooled could comprise any equipment that requires both electrical power and cooling. For example, the device to be cooled could comprise a building interior (i.e. air conditioning) with the electrical power being used to provide electrical power to the building. 

1. A combined refrigeration and power plant comprising: an internal combustion engine; a refrigerator driven by the internal combustion engine and configured to refrigerate a provide working fluid of a combined refrigeration and power generation cycle; a refrigerated working fluid storage unit configured to store working fluid produced by the refrigerator; a first heat exchanger arrangement configured to exchange heat between a device to be cooled and the working fluid; a second heat exchanger arrangement configured to exchange heat between the working fluid downstream of the first heat exchanger in the combined refrigeration and power generation cycle and waste heat from the internal combustion engine; an electrical generator; and a generator turbine configured to receive heated working fluid from the second heat exchanger arrangement, and configured to power the electrical generator.
 2. A power plant according to claim 1, wherein the refrigerator is configured to liquefy the working fluid prior to delivery to the refrigerated working fluid storage unit.
 3. A power plant according to claim 1, wherein the internal combustion engine comprises one or more of a gas turbine engine, a reciprocating engine and a rotary engine.
 4. A power plant according to claim 1, wherein the second heat exchanger arrangement comprises a plurality of heat exchanger matrices, each being configured to exchange heat between the working fluid and a separate heat source of the internal combustion engine.
 5. A power plant according to claim 4, wherein the second heat exchanger arrangement comprises a first matrix configured to exchange heat between engine cooling water and the working fluid and may comprise a second matrix configured to exchange heat between engine cooling oil and the working fluid.
 6. A power plant according to claim 4, wherein the reciprocating engine comprises a turbocharger and may comprise an aftercooler.
 7. A power plant according to claim 6, wherein the second heat exchanger arrangement comprises a third exchanger matrix configured to exchange heat between the turbocharger aftercooler and the working fluid, and may comprise a fourth heat exchanger matrix configured to exchange heat between the turbocharger compressor outlet and the working fluid, and may comprise a fifth heat exchanger matrix configured to exchange heat between the turbocharger turbine inlet and the working fluid.
 8. A power plant according to claim 1, further comprising a third heat exchanger arrangement configured to exchange heat between working fluid downstream of the working fluid storage unit and upstream of the first heat exchanger, and working fluid downstream of the generator turbine and upstream of the working fluid storage unit.
 9. A power plant according to claim 1, wherein the internal combustion engine comprises an internal combustion engine drive shaft mechanically coupled to the generator turbine.
 10. A power plant according to claim 1, wherein the refrigerator comprises an air cycle machine refrigerator comprising a Brayton cycle machine comprising a compressor configured to compress air, a turbine configured to expand compressed air, the compressor and turbine being coupled by an air cycle machine shaft, and a fourth heat exchanger configured to exchange heat between air downstream of the compressor and upstream of the turbine, and a cold sink.
 11. A power plant according to claim 10, wherein the air cycle machine shaft is coupled to one or more of the internal combustion engine drive shaft and an electric motor.
 12. A power plant according to claim 1, wherein the working fluid storage unit comprises a pressure vessel configured to accept working fluid downstream of the refrigerator, and deliver working fluid to one of the first and the third heat exchanger.
 13. A power plant according to claim 1, wherein the working fluid storage unit comprises a separator configured to separate liquid and gaseous working fluid phases.
 14. A power plant according to claim 1, wherein the working fluid comprises one of atmospheric air and supercritical carbon dioxide. 